My 91 w150 318 with 494k miles has been acting up lately. I live in the high desert and its been around 20-30 degrees lately. The problem I have is it was absolutely no power sometimes. It comes and goes randomly. One day its fine on the work and at lunch its barely driveable. I was thinking maybe a coolant temp sensor is faulty but its just a guess. I have ohmed it yet but the connection seems to be good. The plugs wires cap and rotor are only a year old. The fuel filter is a year old and the air filter is good. There's no vacuum leaks and the hoses are good. Also the iac is bad and disconnected at the moment but its set up with the screw backed all the way out so the idle is normal. Any thoughts? I need this fixed before I drive home for Xmas so any ideas will be helpful thanks.

 

have you used a different gas station lately. could be some bad gas.

 

No I always use chevron and it only does it when the temperature outside is cold. When I go home from work it usually runs fine. It's the the cold mornings and cold early afternoons is when its the worst. Letting the engine reach normal temp before driving doesn't make a difference either.

 

You may be having an injector that freezes up when cold. When it is doing this look down inside the throttle body while the truck is running. At the base of each injector you should see a fine cone of fuel. The cone should be solid and even with no gaps or streams. The base of the cones should touch the sides of the throttle body throat.

 

If that's the case wouldn't the problem go away when the engine warmed up?

 

Maybe, maybe not. It isn't that hard to check. The injectors reside in the coolest part of the engine. Just because the engine warms fairly quickly doesn't mean the fuel and intake air do.

 

Youve got a point here. Try some iso heet (red bottle) it should be put in at least once a month when its below freezing in your fuel to prevent fuel pump and injectors from freezing up or becoming restricted. And try to not let gas get below a 1/4 tank. And they might just be worn out by now. Almost 500k did you say?

 

I'll try that right now I got about half tank and yes its at 493983 right now. When I get off work I'm goin to check the injecter spray and check it again when I goto work when its cold.

 

So last nite I replaced the coolant temp sensor and added so heet and this morning it was 25 degrees and she ran like a champ. Hope that was all that was wrong.

 

Its good stuff for under 4 dollars a bottle. Do it every fill up for the next three times. then about once to twice a month when its cold. Glad I might've helped. Had to do the same. Let me know if its different. Best of luck!